The present invention relates to a wireless communication system for a vehicle that performs various types of control through wireless communication between a portable device and a vehicle.
As one such type of wireless communication system for a vehicle, a remote keyless entry system (an RKE system) has been known. The system allows locking or unlocking vehicle doors through manipulation of a switch mounted in a portable device. Conventionally, a system described in Japanese Laid-Open Patent Publication No. 2007-224663, for example, is known as one such RKE system. In this RKE system, each time a switch in a portable device is manipulated by the user, the value of a portable device rolling code is incremented and a wireless signal including the rolling code and a portable device identification code (ID code) is transmitted from the portable device. The wireless signal is received by a receiver mounted in the vehicle. The receiver then transmits the received wireless signal to a controller, which is installed also in the vehicle. After receiving the wireless signal, the controller compares the portable device ID code in the wireless signal with a vehicle ID code stored in a memory mounted in the controller. If the controller determines that the two ID codes match each other through the comparison, the controller compares the portable device rolling code in the wireless signal with a rolling code stored in the memory of the controller. If the portable-device rolling code is greater than the vehicle rolling code and the difference between the rolling codes is less than a predetermined threshold value, the controller determines that the portable device has been authenticated. The controller then actuates a door lock mechanism, which is mounted in each door of the vehicle, to selectively lock and unlock the door. Also at this stage, the controller stores the value of the portable device rolling code in the wireless signal by means of the memory as an update of the vehicle rolling code.
Normally, a wireless signal transmitted from a portable device can be intercepted by a third-party. In the above-described RKE system, even if a wireless signal from the portable device is intercepted by a third-party, the vehicle rolling code can be set to a value greater than the portable device rolling code carried by the intercepted wireless signal once the user locks or unlocks the doors of the vehicle using the certified portable device. As a result, even if the third-party transmits the intercepted wireless signal to the vehicle, authentication of the portable device is not established in the vehicle, and the doors of the vehicle are not unlocked. This prevents the third-party from unlawfully entering the passenger compartment and ensures a high level security for the vehicle.
However, in the RKE system, a wireless signal from the portable device may not be adequately received by the receiver in the vehicle if there is noise that can be received by the receiver. In this situation, the doors of the vehicle cannot be locked or unlocked even if the user turns on the switch of the portable device. This only updates the portable device rolling code without updating the vehicle rolling code. As a result, if a wireless signal sent from the portable device is intercepted by a third-party under this circumstance, the intercepted wireless signal includes a rolling code that is greater than the vehicle rolling code. In this case, if the vehicle moves to a site unaffected by the noise, for example, and then the third-party transmits the intercepted wireless signal to the vehicle at the site, authentication of the portable device will be established. The doors of the vehicle thus may be opened. This makes it impossible to prevent the third-party from unlawfully entering the passenger compartment.
Therefore, since the level of security in the conventional RKE system may decrease in a circumstance where there is noise that can be received by the receiver, the RKE system has room for improvement.